Washington: Defending the controversial phone and internet surveillance programmes of the US, a top American lawmaker backed the stand of the country's leaders and said it had prevented several terrorists' attacks and helped in nabbing David Headley, the 26/11 Mumbai attacks convict.

Congressman Peter King, Chairman of the Counterterrorism and Intelligence Subcommittee of the House Homeland Security Committee, said so during a Congressional hearing.

"The Director of National Intelligence (DNI), General (James) Clapper, has revealed that Headley's terror ties were discovered through the same National Security Agency programs that have come under criticism in past days," King said during the hearing which debated the threat being posed by LeT for a Mumbai type attack on the US.

Earlier, the Senate Intelligence Committee Chair, Senator Dianne Feinstein, had also described capture of Headley one of the successes of the internet tapping program of the US.

However, investigative journalist Sebastian Rotella, who has done a series of investigative reporting on the Mumbai terrorist attack, disputed the arguments being made by top US intelligence officials and lawmakers.

“A closer examination of the case, drawn from extensive reporting by ProPublica, shows that the government surveillance only caught up with Headley after the US had been tipped by British intelligence. And even that victory came after seven years in which US intelligence failed to stop Headley as he roamed the globe on missions for Islamic terror networks and Pakistan's spy agency," Rotella wrote on a website.

"Supporters of the sweeping US surveillance effort say it's needed to build a haystack of information in which to find a needle that will stop a terrorist. In Headley's case, however, it appears the US was handed the needle first — and then deployed surveillance that led to the arrest and prosecution of Headley and other plotters," he wrote.

"The failure here is the failure to connect systems," said a US law enforcement official who worked on the case but is not cleared to discuss it publicly, reported a website. "Everybody had information in their silos, and they didn't share across the silos. Headley in my mind is not a successful interdiction of a terrorist. It's not a great example of how the system should work," the official was quoted as saying.